Encased resistor unit



Oct. 10, 1944. c. M. OSTERHELD' ENCASED RESISTOR UNIT Filed Nov. 2, 1942IN V EN TOR. ULARK/VOSTERHHB BY v ATTORNEY Patented Oct. 10, 19442,366,266 ENCASED nnsrs'roa UNIT Clark M. Osterlield, Stoughton, Wis.,assignor i-o McGraw Electric Company, Elgin, 111., a corporation ofDelaware Application November 2, 1942, Serial No. 464,208

8 Claims.

My invention relates to electric resistor and electric heating units andamong its objects are the following:

To provide a relatively simple and inexpensive encased resistor orheating unit having a minimum number of parts; to provide a resistor orheating unit having a relatively thin.inorganic electric-insulatinglayer or coating between the resistor and the outer casing; to provide aheating unit having a relatively small heat storage mass; to provide aheating unit so designed and constructed that the resistor conductor canbe operated at relatively low temperature to thereby provide a heatingunit which will have a long life and to provide a heating unit that willhave a relatively high break-down voltage and that shall permit of beingformed into any suitable or desired shape for application to a device ora mass to be heated.

Other objects of my invention will either be apparent from a descriptionof several forms embodying my invention or will be set forth in thespecification and particularly in the appended claims. v

In the drawing,

Figure l is a fragmentary view in perspective of a tubular casing usedin my improved resistor or heating unit,

Fig. 2 is a view of the element shown in Fig. 1

, but in partly flattened condition,

Fig. 3 is a fragmentary view of a metal sheath to be associated withtheouter tubular casing shown in Fig.

Fig. 4 is a view in perspective of the tubular casing of Fig. 2 with twometal sheaths inserted therein and a flat resistor unit being insertedinto the sheaths,

Fig. 5 is an end view of Fig. 4 showing the resistor in laterallyarcuate form to more com: pletely fill the space within the sheaths inthe tube when the tube is finally completely flattened,

Fig. 6 shows the parts of Fig. 5 completely flattened,

Fig. 7 shows a flat convoluted wire resistor being inserted into atubular casing having-one sheath therein,

Fig. 8 shows a sheath made of a flat helically wound strip,

Fig. 9 is an end view thereof,

Fig. 10 shows the element of Fig. 8 in partly flattened condition, and,

Fig. 11 shows the helically-wound sheath inserted into an outertubular-casing member.

Referring to Fig. l oi the drawing, I have there illustrated aninitially substantially circular-outer casing 2| which, while preferablymade of metal, need not necessarily be of such material. It may be madeof any suitable high-temperature resisting, heat-conducting substanceable to withstand the influences and conditions which an encasedresistor or heating'unit will meet with in actual operation. I

Referring to Fig. 3 of the drawing, I have there shown a sheath member23 which was initially of flat strip shape but was formed on a rod or tosubstantially circular shape and has been partly flattened tosubstantially the shape shown in Fig. 3 of the drawing. This sheath ismade of a relatively very thin strip of aluminum or of a suitablealuminum alloy and both surfaces thereof, or all of its outer surface,is provided with an integral, inorganic, coherent, heat-conducting, hightemperature-resisting and electric-insulating coating of the kind nowwell known in the art and sometimes called anodic coatings. Reierencemay be made to Patent No. 1,526,127 for one of the many differentmethods which may be used to produce such a coating.

'while the above identified patent discloses the use of an electrolyticmethod, I do not desire to be limited thereto since the so-calledimmersion method may be used whereby to provide a relatively thincoating having the above mentioned characteristics produced thereon.Since the member 23 isto withstand some change in shape or form,it isdesirable that the electric-insulating coating be able to follow thechanges of shape on the strip on which it was produced and I may use anysuitable or desirable method now well known in the art to provide suchan electricinsulating coating. Instead of using a single sheath, I mayuse two strips, one against the respective sides of the single layerresistor, each sheath strip coated on at least that side engaging theresistor.

For purposes of illustration 1 may mention that the thickness of thestrip 23 constituting the I here shown an outer, partly flattened casing2i sheath may be on the order of .015" and that the thickness of theelectric-insulating heat-conducting coating may be on the order of.004". It is possible to provide coatings oi a thickness as abovementioned or of a greater thickness and itis obvious that with aproperly produced coating of this kind, the break-down voltage will begreater with greater thickness oi. the coating.

Referring now to Fig. 4 of the drawing, I have and a plurality oisheaths 23 and 25, one inside of the other, together with a resistorconductor Further,

conductor 29 artiallly inserted therein.

21 partly inserted into the sheaths and the cas- The resistor conductor21 consists of an initially solid strip of resistor material such asNichrome or of any other resistor material, of a suitable thickness andof a width such that it will extend substantially all the way laterallyof the finally formed outer casing and the sheaths therein. The resistorconductor 21 is provided, in a manner now well known in the art, withlaterally-extending lits which alternately extend to the opposite sidesor edges thereof.. It is, therefore, possible by selection of thethickness and the width of the resistor conductor 21 and the number, thedistance between and the width of the lateral slits therein, to provideany desired ohmic resistance in a resistor conductor of this kind.

It will be noted that the resistor conductor 2'5, in that part thereoflocated in or entering the sheaths in the outer tubular casing, may beslightly bent laterally thereof, as is shown in Fig. 5 of the drawing,and this is done in any suitable or desired manner to provide a singlelayer resistor conductor which is of substantially the same width as thespace provided within the sheath or sheaths when the outer tubularcasing 2i is finally substantially completely flattened, as is shown inend view in Fig. 6 of the drawing. A construction of this kind providesa relatively very short heatfiow path from the resistor to the sheath orsheaths and from there to the outer tubular casing since, as abovenoted, the thickness of the sheaths is very small.

Referring now to Fig. 7 of the drawing, I have there shown an outertubular casing 2| having a single sheath 23 therein and having aresistor This resistor conductor consists of a strand or wire which hasbeen bent into substantially parallel, laterally-extending convolutions,as shown in Fig. 7 of the drawing, and it is obvious that the distanceor pace between adjacent convolutions may be any desired value inaccordance with the desired ohmic resistance of such a resistor orheating unit.

While I have shown a sheath of initially strip form which has beenshaped laterally thereof to conform to the shape of the outer tubularcasing, I am not limited thereof and have shown in Figs. 8 to 11inclusive a somewhat different form of sheath. For this purpose I use arelatively narrow and thin strip 3| of aluminum or of an aluminum alloyand Wind the same to helical-coil form. A coating of the kindhereinbefore described as provided on the sheath 23 and on the sheath25,-. if more than one sheath is used, is also provided on sheath 3| andif desired the outer tubular casing 2| may be partly flattened, as shownin Fig. 11, and the sheath 3! may also be partly flattened, as shown inFig. 10, after which the sheath is inserted in the tube 2|. However, itis to be understood that the sheath in the form shown in Fig. 9 may beinserted into the unfiattened, substantially circular casing 21, afterwhich the-two members may be partly flattened to the shape shown in Fig.11 after which any kind of a single layer resistor member shown, in Fig.4 or in Fig. '7 or any other equivalent shaped resistor may be insertedtherein, after which the entire assembly is flattened to substantiallythe shape shown in Fig. 6 of the drawing.

It is evident that I provide an outer tubular metal casing which, whilepreferably made of metal such as aluminum, need not be constituted ofsuch material, having therein a sheath of any suitable form made of verythin aluminum and which sheath is provided with a coating ofelectric-insulating characteristic on at least its inner surface. Itis,of course, obvious that both the inner and the outer surfaces of thesheath may have such a coating thereon and since the thickness of anysuch one coating isivery small, the additive thickness of two coatingswill not be too great to seriously affect or change the inherentlyrelatively low thermal reluctance provided by the sheath 23 or thesheath 3!.

It is to be understood that the resistor or heat ting unit thus fardescribed may be formed into any suitable or desired shapeto either beclosely cooperatively associated with an appliance, or a mass to beheated, but this is generally already well known in the art and myinvention relates more particularly to the elements hereinbeforedescribed.

Various modifications may be made in the systern embodying my inventionas herein shown and described and all such modifications clearly comingwithin the. scope of the appended claims are to be considered as beingcovered thereby.

I claim as my invention:

1. An encased flat resistor unit comprising an elongated convolutedsingle layer metallic resistor strand, a metal lining member engagingboth sides of the resistor and having on its entire surface an integral,inorganic, heat-conducting, high temperature-resisting,lectric-insulating coating and a flat tubular metal casing around theliner to hold the latter in close heat-conducting engagement with theresistor and with the casing.

2. An encased fiat resistor unit comprising an elongated convoluted;single layer metallic resistor member, a metal lining'member e ing bothsides of the resistor member, that part of the surface of one of saidmembers engaging the other member having thereon an integral, inorganic,heat-conducting, high temperatureeresistin electric-insulating coatingand a flat tubular metal casing around the lining member to hold thelatter in close heat-conducting engagement with the resistor and withthe casing,

3. An encased flat resistor unit comprising an elongated convolutedsingle layer metallic resistor member, an elongated liner membertherefor consisting of a strip of metal bent laterally on itself tosurround the flat resistor member, one of said members having on thatpart of its surface enga ed by the other member an integral, inorganic,heat-conducting, high temperature-resisting electric-insulating coatingand a flat tubular metal casing around the liner member holding thelatter in close heat-conducting engagement with the resistor member andwith the casing.

4. An encased flat resistor unit comprising an elongated convolutedsingle layer metallic resistor member, an elongated liner membertherearound consisting of a narrow strip of thin metal wound in helicalcoil shape. and engaging both sides of the resistor member, one of saidmembers having on that part of its surface engaged by the other memberan integral, inorganic, heat-com ducting, high temperature-resisting,electric-insulating coating. and a flat tubular metal casing around theliner member holding the latter in close heat-conducting engagement withthe resistor member and with the casing.

5. An encased fiat resistor unit comprising an elongated convolutedsingl layer metallic resistor member, metal lining member around theresistor member and engaging both sides thereof and a flat tubular metalcasing around the liner member holding the latter in closeheatconducting engagement with the resistor member and with the casing,the surface 01' the resistor, of the lining member and the inner surfaceof the casing having thereon an integral, inorganic, heat-conducting,high temperature-resisting and electric-insulating coating.

6. An encased fiat resistor unit comprising an elongated flatsingle-layer metallic resistor member, an elongated liner memberconsisting of a strip of thin metal bent laterally of itself toprotectively surround the resistor member and a flat tubular metalcasing around the liner member holding the latter in closeheat-conducting engagement with the resistor member and with the casing,the surface of the resistor and of the liner member having thereon aninorganic, integral, heatconducting, high temperatureresistingelectrio-insulating coating.

which the inner surface of the casing also has thereon an integral,inorganic, heat-conducting, high temperature-resisting,electric-insulating coating.

8. An encased flat resistor unit comprising an elongated convolutedsingle-layer resistor member of aluminum, an elongated liner membertherearound consisting of a narrow strip of thin aluminum having athickness on the order of .015" wound flat-wise in helical coil shapeand engaging both sides of the resistor and a flat tubular aluminumcasing around the liner member holding the latter in closeheat-conducting engagement with the resistor and with the casing,

7. A resistor unit as set forth in claim 4 in the inner surface of thecasing and the entire surface of the liner and of the resistor havingthereon an integral, inorganic, heat-conducting, hightemperature-resisting electric-insulating coating, the thickness ofwhich is on the order of CLARK M. OSTERHELD.

